Adjustment-facilitating device for use with a microphone and volume controller

ABSTRACT

A device for facilitating correlation between the values, sound source distance, sound source volume and gain control setting, of an electroacoustical system including a microphone and an amplifier having a gain control, when two of these values are known, comprises a scale support carrying, in mutually fixed coordination, a first scale representative of the setting of the gain control, and at least one other scale representative of the distance of the sound source from the microphone. A slide on the support is movable along the scales and has a first indicator cooperable with the first scale and second indicator elements cooperable simultaneously with at least three adjacent indicia of each other scale. The device may comprise a unit physically independent of the microphone and the gain control, incorporated with the microphone, or incorporated with the gain control.

United States Patent [54] ADJUSTMENT-FACILITATING DEVICE FOR USE WITH AMICROPHONE AND VOLUME 1,444,381 2/ 1923 Landenberger 235/61 B 1,560,59911/1925 235/61 8 2,118,773 5/1938 235/83- 3,117,722 1/1964 235/64.72,788,765 4/1957 116/129 2,948,259 8/1960 Frost et al 116/1 36.5

FOREIGN PATENTS 1,206,020 12/ 1965 Germany 179/1 V PrimaryExaminer-William C. Cooper Attorney-Toren and McGeady ABSTRACT: A devicefor facilitating correlation between the values, sound source distance,sound source volume and gain control setting, of an electroacousticalsystem including a microphone and an amplifier having a gain control,when two of these values are known,comprises a scale support carrying,in mutually fixed coordination, a first scale representative of thesetting of the gain control, and at least one other scale representativeof the distance of the sound source from the microphone. A slide on thesupport is movable along the scales and has a first indicator cooperablewith the first scale and second indicator elementscooperablesimultaneously with at least three adjacent indicia of each other scale.The device may comprise a unit physically independent of the microphoneand the gain control, incorporated with the microphone, or incorporatedwith the gain control.

CONTROLLER 5 Claims, 14 Drawing Figs.

[52] U.S.Cl. 179/1 A, 179/2 R, 235/87 R, 179/179 [51] lnt.Cl. G06c 3/00[50] FieldulSearch 179/1,1A, 179,153,147,1V,121,158,2;235/61B,79.5, 87;116/136.5

[56] References Cited UNITED STATES PATENTS 924,406 6/1909 Walker 235/61B l l I H I l l JILHI l l PATENTED SEP 1 4 l9?! SHEET 3 OF 3 FIG. ll

FIG. IO

INVENTOR. E R N 5T PL E S 5 BY 0M6 Lm I ADJUSTMENT-FACILITATING DEVICEFOR USE WITH A MICROPHONE AND VOLUME CONTROLLER BACKGROUND OF THEINVENTION As a result of the increasing widespread use ofelectroac'oustic installations in everyday life, technically unskilledpersons are increasingly confronted with such installations.Consequently, it is, desirable to simplify the operation of suchinstallations as far as possible, so improper operation or failures, dueto wrong adjustments and the like, may be precluded. I I y I Duringon-the-spot report's recorded by a single operator or reporter, it isdifficult to continuously control the amplifier of a'tape recorderor thelike so that excessive volume fluctuations, during the recording, willbe avoided. Particularly when sound is to be received from sound sourcesat different distances, for example, during conversation with severalpersons, it is nearly'impossible to conduct the interview and at thesame time to watch the level meter of a tape recorder. Nevertheless, toobtain a' usable recording, the reporter must exercise care that thedistance from the'microphone to the speaker remains the same as far aspossible. Even if this care is taken, it is still nearly impossible totake into account or consideration variations. in speech volume.

SUMMARY OF THE INVENTION This invention relates to sound recording and,more particularly, to a novel adjustment facilitating device for use incor- I relating the setting of a gain control and the sound'input levellevel control during transmission of sound events at differentdistances'froin a microphone are substantially simplified. For thispurpose, the invention arrangement enables the provision of satisfactoryori-the spot reports and the like by a single operator and without theneed of expensive automatically controlled amplifiers.

To this end, the invention device indicates, for a given position orsetting of the gain control or volume controller, the proper distancesbetween sound sources and the microphone in the case .of loud, mediumand low sound sources, and indicates, for a given distance between asound source and the microphone, the required setting of the gaincontrol, this being effected without necessity for a recording levelindicatOL.

, .To explain the invention, it may be assumed that the amplification isdefined by a given factor which is constant. In this case, theadjustment-facilitating device of the invention can comprise a simplerange scale, which may be straight or circular, and which is provided atsuitable points with marks having the inscriptions low, medium andloud." The simple adjustment facilitating means will indicate thedistance I necessary to be maintained between the microphone and a soundsource having a givenintensity.

The device of the invention may also take into account the amplificationfactor, which is determined by the setting of a gain control. in thiscase, the invention is based on the fact that there is a direct relationbetween the amplification and the distance between the sound source andthe microphone. Thus the nearer the sound source is to the microphone,the lesser may be the required amplification. To take the foregoing intoconsideration, the invention device is characterized in that a visualfunctional relation is established between a scale and the like,provided with distance or sound intensity indications, and the settingsorpositions of a movable controller or indicator which controls orindicates the gain of the sound recording installation.

In a first and simple embodiment of the invention, theadjustment-facilitating device comprises two scales, a first scaleprovided with figures or symbols relating to the settings of the gaincontrol and a second scale juxtaposed to the first scale and providedwith distance indications so that the required distance from the soundsource to the microphone can be read for any given setting of the volumecontroller, and the correct setting of the controller for any givendistance from the sound source to the microphone is directly apparent.In this embodiment of the invention, the intensity of sound at thesource is not taken into consideration.

In another embodiment of the invention, the intensity of the soundsource is taken into consideration by providing a movable slider betweenthe two scales and having one. indicating mark on the side adjacent tothe volume control scale and at least three marks on its side adjacentto the distance scale. These latter three marks correspondtothree soundintensity values or levels at the sound source. I v,

In order that the device of the invention may be used with differenttape recorders and different microphones, the scales, while normallyfixed, can be relatively displaced by a certain amount for adaptation todifferent applicances. Additional marks, or separate scales, may beprovided to indicate the distances betweenthe sound source and themicrophone when used outdoors or indoors, because different gain valuesare required in each instance. I

In practice, the microphone may be used to pick up sound from a mediumintensity source at a certain distance before the actual recording, andthe amplification of the sound recorder may be adjusted so that thelevel meter indicates a normal level. The two scalesof thesimplestembodiment of the invention are then moved relatively until thescale value corresponding to the setting of the volume controller is'inregistry with that point of the distance scale corresponding to thedistance from the microphone to the sound source used in the test.

When the distance from the sound source to the microphone is suddenlychanged, a brief examination of the adjustment-facilitating device ofthe invention will suffice to determine immediately the now requiredsetting of the gain control of the sound recorder. This position can beset before sound-is received over the newdistanceJWhen the relativepositions of the two scales have been established for a givencombination of sound recorder and microphone, the correct setting of theapplicances can be obtained at any time without a transmitting test, andthe scales may be fixed relative to each other.

In the embodiment of the invention including a slider, as mentionedabove, the mode of operation is basically the same. The provision of theslider enables a determination of the range in which useful recordingsare obtained, without need for a change in the setting of the gaincontrol, ,and a compensation of volume fluctuations by a change of thedistance from the sound source to the microphone in accordance with theindications given by the adjustment-facilitating device. The device maybe embodied in various forms. For example, linear scales are notessential and the scales may be circular, such as common with circularslide rules. Any sliders which are used may be designed in accordancewith the two configurations and in a known manner. The device may bemade as a separate article which can preferably be carried convenientlyin the pocket, or the device may consist of a pendant or the like.

Alternatively, the device may be mounted directly on the microphone orits housing, and this concept may be embodied in various ways. In oneembodiment, the microphone housing may comprise a solid of revolutionwhich is embraced by the two scales which are conjointly rotatable andwhich can preferably be adjusted relative to each other with a certainfrictional restraint. The corresponding marks are provided on themicrophone housing. This particular embodiment of the invention is veryadvantageous because the device cannot be lost and can easily beinspected when required.

lt is desirable to indicate the distance between the microphone and thesource of sound not only in meters but also in feet and even in paces,because a measuring tape is not always available and pacing will providesufficiently accurate results. In an embodiment of the invention, threeannular distance scales are arranged in juxtaposed position on themicrophone body and respectively indicate distances in meters, distancesin feet, and distances in paces.

The three scales are covered by a sleeve surrounding the microphonehousing, and which is rotatably and slidably mounted thereon, thissleeve being formed with a window or aperture permitting viewing of onlyone scale at a time. During use, the sleeve is displaced longitudinallyof the microphone body, or parallel to the axis of the solid ofrevolution, until the selected one of the three scales becomes visiblein the window, detent devices being provided to prevent an unintendeddisplacement of the sleeve during use. The scale representing thesettings of the gain control is disposed outside the sleeve andcooperates with a mark provided on the sleeve. When the distance-scalehaving the desired units has been selected by a longitudinaldisplacement of the sleeve, the device is used in the same way asdescribed above. If the microphone is noncircular in cross section, thering-or sleeve may be elastic to closely embrace the microphone housingin the nature of an elastic belt or the like.

In accordance with the invention, the adjustment-facilitating means ordevice may be provided on the amplifier or tape recorder. In thesimplest case, a rotary knob is used and is provided with a distancescale in registry with suitable indicating marks provided on the housingof the amplifier or the tape recorder.

In further accordance with the invention, the adjustmentfacilitatingdevice may alternatively be combined with a control slider, in whichcase the scales can be provided on both sides of the path of the slider.The knob of the slider can either be provided with suitable indicatingmarks or can be designed as a pointer.

In yet another embodiment of the invention, the housing of themicrophone is provided with a series of small lamps preferably indifferent colors, and these lamps correspond to significant points of adistance scale and indicate the setting of the gain control and therelated distance from the sound source to the microphone.

In still another embodiment of the invention, the volume controller maybe incorporated directly in the microphone housing and this embodimentincludes the same features as the embodiment in which theadjustment-facilitating device or means is directly combined with thegain control or volume setting member in an amplifier housing.

An object of the present invention is to provide anadjustment-facilitating device for use with a microphone and a gaincontrol. g

Another object of the invention is to provide such a device enablingsatisfactory on-the-spot reports and the like by a single operator ofsound recording equipment and without the need of expensiveautomatically controlled amplifiers.

A further object of the invention is to provide such a device whichindicates, for a given setting of the gain control, the correlateddistance from the sound source to the microphone in the case of loudsound sources, medium sound sources, and low sound sources.

Yet another object of the invention is to provide such a device whichindicates, for a given distance from the sound source to the microphone,the correlated setting of the gain control and without need for a levelindicator.

A further object of the invention is to provide such a device comprisinga simple range or distance scale provided at suitable points with marksindicating low sound level, medium sound level, and high sound level.

Still another object of the invention is to provide such a device whichtakes into consideration the amplification factor of the amplifier ofthe sound recorder.

A further object of the invention is to provide such a device in which avisual functional relation is established between a scale provided withdistance or sound intensity indications and the position or setting of amovable recording volume controller or indicator which controls orindicates the gain of a recording device or the like.

Another object of the invention is to provide such a device which may beincorporated with a microphone or which may be incorporated with anamplifier or sound recorder.

A further object of the invention is to provide such a device includinga scale indicating gain control setting and at least one scaleindicating the distance between a microphone and a sound source,together with a slider establishing correlation between the two scales.

Another object of the invention is to provide such anadjustment-facilitating device which can be made as a separate articlefor convenient transport.

BRIEF DESCRIPTION OF THE DRAWINGS For an understanding of the principlesof the invention, reference is made to the following description oftypical embodiments 7 thereof as illustrated in the accompanyingdrawings.

In the drawings:

FIGS. 1 and 2 are elevation views ofa device embodying the invention anddesigned as a separate article;

FIG. 3 illustrates a device embodying the invention as combined with amicrophone;

FIG. 4 is a partial side elevation view illustrating the device of FIG.3 as provided with a slider;

FIG. 5 is a view similar to FIG. 4, but in which the device comprises aplurality of distance scales using respective different measuring units;

FIG. 6 is an elevation view of a microphone provided with anotherembodiment of the device according to the invention;

FIGS. 7, 8 and 9 are partial elevation views illustrating modificationsof the arrangements shown in FIG. 6;

FIGS. 10 and 11 are partial elevation or plan views illustrating thedevice embodying the invention as incorporated in an amplifier or taperecorder;

FIG. 12 is an elevation view of a device embodying the invention, asincorporated in a microphone, and including a series of lamps ofrespective different colors;

FIG. 12a is a schematic wiring diagram related to the arrangement shownin FIG. 12; and

FIG. 13 is an elevation view of a modified form of the invention inwhich a volume control member is incorporated in a microphone housing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, theembodiment of the adjustmentfacilitating device shown therein is in theform of a tablet bearing three scales 4 and a single scale 4a. Scale 4a,bearing the legend VOL, is provided with the numbers 1 to 10corresponding to 10 positions or settings of the gain control. Thescales 4, shown to the right in FIG. 1, represent the distance from thesound source of the microphone in meters (m), feet (f), and paces orsteps (s), respectively, as indicated by the data of the lower end ofeach scale 4a. A slider 2 is mounted for longitudinal slidable movementbetween gain control setting scale 4a and the left hand distance scale4. Slider 2 carries, in three fields the respective inscriptions, LOUD,"NORMAL, and LOW. Each field has a respective arrow 20a directed towarddistance scales 4, and the slider has a single arrow 20b directed towardthe gain control setting scale 40.

In the position of the parts shown in FIG. I, slider 2 indicates that,with the gain control set at position 9, the distance from amedium-intensity sound source to the microphone should be 3 meters for anormal recording level on the tape of a tape recorder. A loud speakerwould require a distance of 5 meters from the microphone, and a lowspeaker a distance of 2 meters. The indicated values do not representactual values, but are only for illustrative purposes.

At the lower end of the device as shown in FIG. I, the word SPEECH"appears over the word TYPE." This means that the adjustment-facilitatingdevice in FIG. 1 indicates the correlated values for speech. For othersound events, such as solo performances, musical recordings, etc., therelations differ from those or speech recordings. In such casing, adifferent adjustment-facilitating device is required, which is suitablefor the particular type of sound to be picked up. However, the slidermay be so designed as to provide an adjustmentfacilitating device ofuniversal utility.

FIG. 2 illustrates the device of the invention as embodied in the formof circular disc carrying circular scales 4. and 4a rather thanrectilinear scales. Slider comprises a sector of a circle, and isrotatable about the center of the scales and formed with an aperture 3constituting a window through which the scales can be read. The upperscale 4 represents distance in meters, and the lower scale 4, which isthe radially outer scale, represents distances in feet. Theadjustmentfacilitating device shown in FIG. 2 has basically the samefunction as that shown in FIG. I, from which latter it differs only inform.

A particularly simple embodiment of the invention is shown in FIG. 3 inwhich two parallel scales 4 and 4a are arranged in juxtaposed positionon a rodshapedgicrophone 1. Scale 4 again represents distances between asound source and the microphone, and scale 40 again represents thesettings of the gain control, as indicated by the representative marksm" and V." The juxtaposed scales indicate immediately the correlateddistance from the sound source to the microphone for a given setting ofthe gain control, and vice versa.

A further development of the embodiment of the invention shown in FIG. 3is illustrated in FIG. 4. Referring to FIG. 4, the slider 2b is in theform of a sleeve provided with a window and slidably fitted on therod-shaped microphone housing I, which latter may be cylindrical orprismatic in cross section. Only a single value can be read from volumecontrol setting scale 40, but the longer portion of the window alignedwith scale 4 enables the operator to read a range of values of thisdistance scale. In the particular case illustrated in FIG. 4, thedistance range from 0.8 m. to 1.5 m. is visible. Thearrangement ispreferably such that, with a given setting of the gain control as isread through the smaller portion of the window 3, that range of thedistance scale in which a satisfactory recording will be obtained willbe visible in the longer portion of the window 3. Alternatively, wiridow3 may be designed to provide a reading within limits corresponding tooptimum distances between loud or low speakers and the microphone, orfor outdoor or indoor use.

FIG. 5 illustrates a further development of the embodiment of theinvention shown in FIGS. 3 and 4, in which a scale of distances in feetis provided in addition to the scale of distancesin meters. For example,the upper scale 4 represents distances in feet and the lower scale 4represents distances in meters. The slider 2c has twowindows 3, onehaving a longer opening coinciding with the scale having distances infeet and the other having a longer portion coinciding with the scalehaving distances in meters, and a respective gain control setting scale4a is operatively associated with each scale 4.

Embodiments of the invention in which the adjustmentfacilitating deviceis provided on the body or housing of a microphone are shown in FIGS. 6,7, 8 and 9. Referring first to FIG. 6, distance scale 4 and gain controlsetting scale 4a are carried directly by the microphone I, on thesurface thereof, and the reference marks associated with the scales,such as the reference mark 20b, are carried on a rotatable ring 2ddisposed between scales 4 and 4a and having the same function as theslider shown in FIGS. 1 and 2.

A different but equivalent embodiment of the device is shown inFlG. 7.The embodiment of the invention shown in a FIG. 7 differs from thatshown in FIG. 6 in that the scales 4 and 4a are covered by an extensionor sleeve 2: of rotatable ring 2d, so that the scales can be read onlythrough windows 3 in the sleevelike extension.

It is expensive to provide scales directly on the surface of themicrophone housing, and this expense may be reduced or eliminated by thearrangement of FIG. Referring to FIG. 8, scales '4 and 4a are providedha a rotatable ring 2f, and fixed indicating reference marks 20a and 20bare provided on the microphone housing. The arrangement of FIG. 8 hasthe advantage that it is relatively simple to make a rotatable ring 2],comprising two parts which are relatively adjustable, so that theadjustment-facilitating device can easily be calibrated in the mannerdescribed above.

A particularly refined embodiment is shown in FIG. 9 as including threedistance scales 4, respectively calibrated in meters, feet, and paces orsteps. The scales are juxtaposed with each other on a cylindricalportion of the microphone housing I. A sleeve 2 is provided and isdisplaceable longitudinally and rotatably relative to the cylindricalportion of housing I. Sleeve 2 has only a single window 3 through whichonly one scale 4 can be read at a time. A detent device (not shown)enables an exact setting of the sleeve into alignment with a selectedscale, and also prevents an unintended displacement to a different scale4. The gain control setting scale 40 is provided on microphone body Ioutside of sleeve 2, and cooperates with an indicating reference mark20b on sleeve 2. When reading window 3 of sleeve 23 has been alignedwith desired distance scale 4, the adjustment-facilitating device isoperated in the same manner as described for the preceding embodimentsof the invention.

As shown in FIGS. 10 and II, the adjustment-facilitating device of theinvention may be structurally combined with the gain control of thesound installation, and such a gain control may be incorporated, forexample, in the amplifier housing or in a tape recorder. Referring toFIG. I0, the knob II for adjusting a gain control 10 is provided with adistance scale 4 and may be provided if desired, with a volume settingscale 4b. In the same manner as previously described, scales 4 and 4bcooperate with indicating mark 201: on the housing containing the gaincontrol and which may be an amplifier housing or a tape recorderhousing.

As shown in FIG. 11, a control slider may be combined with theadjustment-facilitating device. In this case, scales 4 and 4a areprovided on opposite sides of the path of movement of slider knob 12,and slider knob 12 is constructed in essentially with the body orhousing I of a microphone. Referring to these figures, lamps 13,preferably of respective different colors, are mounted in the body orhousing 1 of the microphone and each lamp is associated with a differentrespective distance from the sound source to the microphone, asindicated by the respective numerals alongside each lamp 13. Amultiple-position switch 14, shown in FIG. 12a, is mounted on the sameshaft as the volume controller of the sound installation, so that eachlamp is associated with a certain angular position or setting of thegain control. The embodiment of the invention shown in FIGS. 12 and 12aprovides a particularly convenient and fast reading, and the accuracywhich is obtained is quite sufficient for acoustic purposes. Thedistance values may be indicated on a cover glass for each lamp, so thatthe device becomes particularly suitable for recording on-the-spotreports outdoors and during night hours.

FIG. 13 illustrates a microphone I which contains, in its housing, avolume or gain control setting member I5 for a remote gain control. Asin the embodiment shown in FIG. 6, the knob of the setting member isprovided with a distance scale 4, and a reference or indicating mark 200is provided on housing 1 adjacent the knob. The scales may be coveredwith luminous paint, so that the reporter can work also during nighthours.

The adjustment-facilitating device of the invention is also suitable forappliances and installations provided with automatic volume control,because there are limits to such an automatic control. In analogy tophotographic cameras having an automatic exposure control system, zonesand different colors may be used to indicate in what ranges asatisfactory recording level will be obtained or will'not be obtained onthe sound recording medium.

The invention device provides a fast and a reliable device particularlywhen working with portable sound recorders. Numerous designs may beemployed, and it is not possible to outline specifically all of theembodiments which may be conceived. The device may be very large or verysmall, for example, in the form of a key pendant. it may be structurallysimple or complicated, and may cooperate, for example, with aninstrument having a pointer and distance scale. A deflection of theinstrument will indicate the position or setting of the gain control,and the pointer will then indicate the optimum distance from the soundsource to the microphone.

The instrument may be replaced by a difi'erent indicator such as a smallelectron-beam tube carried directly by the microphone. The gain controlmay also be disposed in the microphone housing. In this case, the entirearrangement would replace the usual level meter. It is sufficient, inuse, to adjust the controller until the pointer assumes the positioncorresponding to the actual distance from the sound source to themicrophone. When this is the case, the optimum recording level will beobtained. This operation may be repeated when the distance from thesound source to the microphone is changed. Compared to the usualindication of the recording level on the microphone, the arrangement ofthe invention has the advantage that it enables a preadjustment of theinstallation so that a sound transmission test is not required. Theadjustment is also faster and more reliable than with the aid of a levelmeter because the values indicated by the adjustmentfacilitating devicehave proved satisfaetbry in practice.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

I. In an electroacoustical system including a microphone and anamplifier having a gain control, a device for the numericaldetermination of one of the values sound source distance, sound sourcevolume and gain control setting, when two of these values are known,said device comprising, in combination, a microphone housing elementhaving a circular cross section; and a cylindrical element rotatablymounted on said circular cross section housing element; one of saidelements carrying two scales each respective to one of said values, andthe other of said element's carrying indicating means cooperable withsaid scales to coordinate said scales with respect to said third value.

2. A device, as set forth in claim 1, characterized in that said housingelement constitutes a scale support; said cylindrical element comprisinga ring rotatably mounted on said microphone housing element and havingan aperture exposing said scales.

3. A device, as set forth in claim 2, characterized in that there are aplurality of a first type of scales each in mutually fixed relationshipwith one of a plurality of a second type scales; said ring having aplurality of apertures each exposing a respective one of said first typeof scales and the associated one of said respective second type ofscales; and each of said second type of scales being calibrated indifferent respective measuring units.

4. A device, as set forth in claim 2, characterized in that said ringincludes a sleeve mounted on said microphone housing element fordisplacement longitudinally of said microphone housing element; therebeing a plurality of a second type of scales, each calibrated indifferent respective measuring units, said second type of scales beingdisplaced longitudinally of said microphone housing element; and saidsleeve being formed with a window exposing only one of said second typeof scales at a time. t

5. A device, as claimed lll claim 2, in which said gain control isincorporated in said microphone.

1. In an electroacoustical system including a microphone and anamplifier having a gain control, a device for the numericaldetermination of one of the values sound source distance, sound sourcevolume and gain control setting, when two of these values are known,said device comprising, in combination, a microphone housing elementhaving a circular cross section; and a cylindrical element rotatablymounted on said circular cross section housing element; one of saidelements carrying two scales each respective to one of said values, andthe other of said elements carrying indicating means cooperable withsaid scales to coordinate said scales with respect to said third value.2. A device, as set forth in claim 1, characterized in that said housingelement constitutes a scale support; said cylindrical element comprisinga ring rotatably mounted on said microphone housing element and havingan aperture exposing said scales.
 3. A device, as set forth in claim 2,characterized in that there are a plurality of a first type of scaleseach in mutually fixed relationship with one of a plurality of a secondtype scales; said ring having a plurality of apertures each exposing arespective one of said first type of scales and the associated one ofsaid respective second type of scales; and each of said second type ofscales being calibrated in different respective measuring units.
 4. Adevice, as set forth in claim 2, characterized in that said ringincludes a sleeve mounted on said microphone housing element fordisplacement longitudinally of said microphone housing element; therebeing a plurality of a second type of scales, each calibrated indifferent respective measuring units, said second type of scales beingdisplaced longitudinally of said microphone housing element; and saidsleeve being formed with a window exposing only one of said second typeof scales at a time.
 5. A device, as claimed in claim 2, in which saidgain control is incorporated in said microphone.